UK - the world's plutonium store?

An unexpected outcome of the Fukushima nuclear disaster is that the UK's Sellafield nuclear site - already the world's biggest plutonium repository - is set to store even more of the radioactive, fissionable metal.

Britain is "very interested in Japan’s surplus plutonium"

Of the world's 260 tonnes of plutonium almost half - 120 tonnes - are stored in the UK, of which 96 tonnes were produced from the UK's own nuclear waste, while 17 tonnes come from Japan and the remainder from other countries.

But this massive plutonium stockpile could soon be joined by more. Another 20 tonnes are expected to be produced from reprocessing operations at THORP (Thermal Oxide Reprocessing Plant), Britain's nuclear waste reprocessing plant at the 6-square kilometre Sellafield nuclear site in Cumbria.

And now the UK is angling to become the repository for another 27 tonnes of Japanese plutonium, 18 of them now in France and 9 of them in Japan..

That's not all. Japan is also building a reprocessing plant in Rokkasho, in Aomori Prefecture, which is due to produce seven tonnes of plutonium a year as it reprocesses Japan's large stocks of nuclear waste. In principle Japan wants to use that plutonium to make new MOX (Mixed Oxide) nuclear fuel to fuel its 50 nuclear power stations.

But with Japan's reactors closed following the Fukushima nuclear catastrophe, the plutonium will need to be stored for some time to come. First the power stations will need to pass new, tougher government safety standards, and second there must be a clear political will to restart the reactors. Neither is guaranteed.

Last year the British Nuclear Decommissioning Authority built a huge plutonium repository at Sellafield, the size of a soccer field, conveniently next to THORP - and more than big enough to take Japan's surplus plutonium as well as its own. The building is 30 metres high, windowless, and surrounded by thick concrete walls and high fences to protect the plutonium inside from terrorists.

The Asahi Simbun has quoted an unnamed official of the British government, who is involved in the new business, as saying that Britain is "very interested in Japan’s surplus plutonium".

With Germany also closing down its nuclear power stations there is also the possibility that German plutonium stocks could end up on Britain's shores - at a price.